Method of making diaphragm



March 4 L. R. BURROUGHS 2,396,824

METHOD OF MAKING DIAPHRAGM Filed Sept. 20, 1943 /6. 5. P/ci 4.

IN V EN TOR.

BY mgf/ Patented Mar. 19, 3946 METHOD OF MAKING DIAPHRAGM Louis R.Burroughs, South Bend, Ind., assignor to Electra-Voice ManufacturingSouth Band, 1115.,

00., Inc.,

a corporation of Indiana Application September 20, 1943, Serial No.503,094

1 Claim.

This invention relates to a method of making diaphragm, and moreparticularly to a method and means for mounting a diaphragm in a soundtransmitting or translating device.

The diaphragm of a sound transmitting or translating device, such as amicrophone, is commonly positioned or seated in the device by mountingmeans engaging the opposite faces of the margin thereof. The diaphragmmust be held by such means in a manner which willnot interfere with fulland free vibration of the diaphragm for true fidelity response thereofto sound waves, impulses or signals imposed thereon. Thus no stressshould be imparted by the mounting means upon the diaphragm.Furthermore, the parts are so delicate or sensitive that even very smalldepartures from a true fit of diaphragm and mounting may result inserious operating disturbances.

Therefore, it is the primary object of this in-- vention to provide amounting which precisely fits the diaphragm.

A further object is to provide a diaphragm mounting which is formed fromthermoplastic material which is fitted to the diaphragm by pressureWhile heated.

A further object is to provide two-part means for mounting a diaphragmby a. uniform perimetrical binding thereof under pressure ample toafi'ord a proper firm seating of the diaphragm and insufiicient tophysically distort the diaphragm or prevent accurate vibratory responseto sounds impinging thereon.

A further object is to provide a diaphragm mounting which serves as aseal against moisture.

A further object is to provide a novel and simple method forconditioning and shaping mounting means to the characteristic of thediaphragm mounted thereby.

Other objects will be apparent from the description, drawing andappended claim.

In the drawing:

Fig. 1 is a transverse sectional view of a microphone.

Fig. 2 is a face view of a mounting ring.

Fig. 3 i an enlarged detail sectional view illustrating the preassembledrelation of the mounting rings.

Fig. 4 is an enlarged detail sectional view illustrating the assembledrelation of the mounting rings to the diaphragm.

Referring to the drawing, wherein application of the invention to amicrophone is illustrated, the numeral I0 designates a two-part hollowmicrophone housing. Each of the housing parts is substantiallycup-shaped. The front part has a front wall II provided with soundpassages I2 extending therethrough, and a thickened marginal wall I 3.The rear housing part has a rear wall I4. a thickened margina1 portionI5 and a central rear off-set I6 in which a pocket or recess, preferablyof frusto-conical shape, is formed for communication with the cavity ofthe housing. A metal liner or button I! fits in said recess or pocket,and a conductor I8 is connected therewith and extend through the housingwall to provide a projecting electrical terminal I9. Screws 20 securethe contacting ma ginal housing parts I3 and I5 together.

A diaphragm 2I formed of a thin fiat disc or plate of metal has acentral frusto conical integral off-set 22 projecting into button I I incoaxial spaced relation thereto. Diaphragm 2| lies in the parting planeof the housing sections, and a pair of similar rings 23 of resilientmaterial are arranged in coaxial relation to off-set 22 at oppositesides of the diaphragm to span the spaces between the diaphragm andhousing walls II and I4. Carbon granules or other suitable conductivegranular material 24 fills the space within the rear ring and engagesthe diaphragm and the button.

Each of the cup-shaped housing parts mounts a diaphragm seating ring 25fitting snugly therein against the thickened marginal housing portionsI3 and I5. These rings are formed of thermoplastic material of thesynthetic resin type of which vinyl resin copolymer, cellulose acetateand acrylics are examples. The inner side face 26 of each ring ispreferably radially or transversely crowned or contoured as illustratedin Fig. 3, and the initial overall thicknes thereof is preferablyapproximately about .010 of an inch greater than the thickness requiredto contact diaphragm 2| at its margin when the device is assembled.Therefore, since the thickness of a diaphragm is in the order of .005 ofan inch, it will be seen that the crowns of the rings project beyond theplanes or faces of the marginal housing portion I3 and I5 which areintended to engage when the microphone is assembled. The diaphragm ispreferably secured to one housing part, as by means of an integraltongue 21 projecting therefrom and imbedded in marginal housing portionI5. The outer end of tongue 21' preferably projects from the housing toform a terminal 28.

To properly condition the parts for assembly of the microphone, andparticularly to reshape or reform the excessively thick or oversizerings 25, the parts are positioned with the rings 25 and diaphragm 2I inproper registering 0r coaxial relation while rings 25 are in a heatedcondition.

2 Pressure is then exerted axiany with the parting faces of marginalhousing portions l3l5 are brought into full face engagement. Theapplication of pressure in this manner reshapes or reforms the rings 25to precisely fit the diaphragm 2|, and entails a flattening of thecrowned ring faces as shown in Fig. 4. The application of pressure iscontinued until the rings have taken a permanent set in this shape. Onematerial of which the rings 25 may be formed i known commercially asVinylite," and when this material is used, satisfactory results areobtained when the same is heated above the softening point, as from 150to 220 or more, Fahrenheit, incident t the pressing operation.

An alternative process is to insert the rings 25 in the housing parts,position the preassembled units in registration with the diaphragmtherebetween, apply pressure to the registeringparts, and heat theregistering parts while maintaining the applied pressure. Thisnecessitates formation of the housing from materials such as metal, orplastics having a substantially higher softening temperature than thematerial of which rings 25 are formed. In some instances it may benecessary to follow a procedure wherein each ring is individuallyreshaped. For instance, a metal ring or plate may engage one surface ofthe diaphragm as pressure is applied to an assembly including said metalplate, the diaphragm, one ring 25 engaging the opposite diaphragm face,and the housing part mounting ring 25. The operation is then repeated toform the face of the ring 25 which is to engage the face of thediaphragm against which the metal plate bore during the first operation.Such a two-step process may be necessitated when the conditions are suchthat simultaneous forming of both rings might introduce distortingstresses in the diaphragm, as when the diaphragm is exceedingly thin andthe opposed rings are not preformed to exact equal thickness. Theprocessing of the diaphragm-engaging parts, including the housing alsoin the one embodiment, provides amounting for the diaphragm which isexactly and precisely fitted to the particular diaphragm to be mountedthereby and to the housing parts which mount the rings. Thus the ringsare reset or reshaped to the exact form required in each instrumentordevice. Assembly of the device. completed by the securing together ofthe housing parts with their marginal ortions in face engagement,eflects a full, firm and uniform positioning engagement of each ringwith the diaphragm margin. This prevents physical distortion of orapplication of stress to the diaphragm, so that the diaphragm may have afull free vibratory response to sounds, impulses or signals impingingthereon. At the same time. the face engagement of rings 25 with thediaphragm is of such character that no moisture can penetratetherebetween, and the microphone or other device is effectively sealedor rendered waterproof at the parting plane or its housing.

While the diaphragm mounting rings 25 have been illustrated as solid,they may be formed of tubular cross section, if desired. Where tubing isemployed, the application of pressure while the ring is heated entailsalteration of the cross sectional shape thereof and conformance ofsurface contours thereof with the diaphragm faces with less pressurethan required with solid rings. Also, the possible adverse effects ofextrusion of the ring material, such as production of a greater area ofcontact of the rings with the diaphragm than desirable, are avoided.

While the invention has been illustrated as applied to a microphone, itis obviously applicable to devices of other types, such as car phonesand to devices sensitive to or for the measurement of pressures.

I claim:

The method of mounting a diaphragm between similar opposed rings in ahousing formed of a pair of recessed parts, consisting of the steps ofinserting oversize thermoplastic rings in said housing parts andpressing said housing parts against opposite faces of a coaxiallyinterposed diaphragm while said rings are heated to a softened state.

LOUIS R. BURROUGHS.

